title: Heck coupling of olefins to mixed methyl/thienyl monolayers on Si(111) surfaces.
abstract: The Heck reaction has been used to couple olefins to a Si(111) surface that was functionalized with a mixed monolayer comprised of methyl and thienyl groups. The coupling method maintained a conjugated linkage between the surface and the olefinic surface functionality, to allow for facile charge transfer from the silicon surface. While a Si(111) surface terminated only with thienyl groups displayed a surface recombination velocity, S, of 670 ± 190 cm s(-1), the mixed CH3/SC4H3-Si(111) surfaces with a coverage of θSC4H3 = 0.15 ± 0.02 displayed a substantially lower value of S = 27 ± 9 cm s(-1). Accordingly, CH3/SC4H3-Si(111) surfaces were brominated with N-bromosuccinimide, to produce mixed CH3/SC4H2Br-Si(111) surfaces with coverages of θBr-Si < 0.05. The resulting aryl halide surfaces were activated using [Pd(PPh3)4] as a catalyst. After activation, Pd(II) was selectively coordinated by oxidative addition to the surface-bound aryl halide. The olefinic substrates 4-fluorostyrene, vinylferrocene, and protoporphyrin IX dimethyl ester were then coupled (in dimethylformamide at 100 °C) to the Pd-containing functionalized Si surfaces. The porphyrin-modified surface was then metalated with Co, Cu, or Zn. The vinylferrocene-modified Si(111) surface showed a linear dependence of the peak current on scan rate in cyclic voltammetry, indicating that facile electron transfer had been maintained and providing evidence of a robust linkage between the Si surface and the tethered ferrocene. The final Heck-coupled surface exhibited S = 70 cm s(-1), indicating that high-quality surfaces could be produced by this multistep synthetic approach for tethering small molecules to silicon photoelectrodes.
authors.affiliation: Beckman Institute and Kavli Nanosciences Institute, Division of Chemistry and Chemical Engineering, 210 Noyes Laboratory, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Leslie E
authors.initials: LE
authors.lastname: O'Leary
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rose
authors.forename: Tina X
authors.initials: TX
authors.lastname: Ding
authors.forename: Erik
authors.initials: E
authors.lastname: Johansson
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Lewis
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D015394:Molecular Structure; D012825:Silicon / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000475:Alkenes; D013438:Sulfhydryl Compounds; D012825:Silicon